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2024 GMC Sierra HD AT4X and Extreme AEV muscle their way into the lineup

The new AT4X variant of GMC's 2024 Sierra HD pickup series officially joins the stable this week, giving pickup truck box-checkers yet another off-road trim to chase. Well, two trims, technically, as GMC took the opportunity to announce that the AT4X will also be offered with an upfit package from American Expedition Vehicles, appropriately named the Extreme AEV Edition that takes its cues from the same package offered on the Sierra 1500 AT4X. And with its introduction, the 2024 GMC Sierra HD lineup is now complete.  GMC's Sierra AT4X models mirror the ZR2 packages offered on the updated Chevrolet Silverado. If you paid any attention at all to the Silverado HD ZR2's introduction earlier this month, you'll be familiar with the formula. Key upgrades include a 1.5-inch factory lift, standard electronic locking rear differential, Multimatic DSSV shocks and 35-inch Goodyear Territory all-terrain tires. It also gets beefier skid plates —  both the steel protecting the transfer case and the aluminum piece up front. With the updated 6.6-liter Duramax diesel, GMC says it'll tow up to 18,500 pounds.  "GMCÂ’s AT4X trim, which will be available across the entire GMC truck lineup, offers customers more premium and capable choices when it comes to ‘do-it-allÂ’ capabilities," said GMC VP Duncan Aldred. "Each model delivers unique strengths, with the all-new Sierra HD AT4X taking it to the max, enabling you to go virtually anywhere, with the towing power to bring your recreational toys, gear or camper along for the journey." And by "do it all," he means all the luxury stuff too, judging by the Obsidian Rush interior, which GMC says includes massaging leather front seats and real ash wood trim. The better from which to feel the shove of the AT4's two available 6.6-liter engines, one a gasoline-burner rated at 401 horsepower and 464 pound-feet of torque, the other a Duramax turbodiesel making 470 horsepower and 975 pound-feet of torque. You'll need the latter if you want to hit GMC's advertised towing capacity.  And don't forget the Extreme AEV Edition, which will surely come with a Denali-rivaling (and still TBA) price tag. The stamped steel bumpers stand out right away, as do the integrated front recovery points and winch mount. The package also adds more skid plates protecting the steering gear and transfer case. Its 18-inch "Salta" wheels are also unique.  GMC says it will be cranking out 2024 Sierra HD AT4Xs and Extreme AEV Editions by the third quarter.

2024 GMC Hummer EV SUV Second Drive Review: Moab made easy

MOAB, Utah — The title of our First Drive of the 2024 GMC Hummer EV SUV included the phrase, "It's big, but this elephant can dance." The truck earned that compliment after a day of squeezing through San Francisco lanes and the slightly-more-commodious back roads in Napa Valley. But an SUV can't be called a supertruck without equivalent mastery on dirt, so GMC led a posse of media to Moab, Utah to run the Hummer's favorite stomping grounds. What happens when you subtract 20 inches of overall length and nine inches of wheelbase from a megafauna pickup? You find the dancing doesn't stop where the pavement ends. Allowed to roam Moab's challenging terrain — and ample room — the SUV is more than ready to do the Hokey Pokey and turn itself around. Admittedly, we knew this from our First Drive of the Hummer SUT two years ago, also performed among Moab's red rocks and red dust. The two variants share the same tricks, and GMC engineers chose Moab for prototype development, so there was no question of successfully navigating the trails. The SUV's simply nimbler about than the SUT. Clearance angles are better all over. Compared to the SUT, the SUV's 49.6-degree approach angle is just 0.1 better, but the 49-degree departure angle is 10.6 degrees better, and the breakover angle is 2.2 degrees better. Having four-wheel steer to rotate the SUV's shorter wheelbase shrinks the already tiny turning circle by 1.7 feet, to 35.4 feet. That's only four feet wider than a BMW i3, but 14 feet more compact than a GMC Sierra Crew Cab with the Short Box. And there are 'only' 15 standard cameras on the SUV, one shy of the 16 cameras in the SUT; the pickup adds an angle on the cargo bed the SUV doesn't have. Our 3X trim packed three motors producing a combined 830 horsepower and 1,200 pound-feet of torque. The $9,995 Extreme Off-Road Package threw on rock sliders with integrated steps that can support 1.5 times the Hummer's weight, full underbody skid plating, two additional underbody cameras front and rear, an electronically locking mechanical front differential for the single motor on the front, a virtual rear differential (programming that makes the two rear motors behave like a locked diff), heavy-duty ball spline half shafts, tow hooks and 18-inch black wheels on 35-inch Goodyear Wrangler Mud-Terrain tires.

GM exploring ways to raise half-ton Duramax diesel tow rating

Lots of truck owners cheered when GM announced fuel economy numbers for the 2020 Chevrolet Silverado with the 3.0-liter Duramax diesel inline-six. Even after Ram let loose its EPA mileage ratings for the 2020 Ram 1500 EcoDiesel, the Chevy oil-burner still took the trophy. The victory was years in the making, GM engineers spending an entire four-year development cycle refining the LM2 Duramax to increase mileage. The tradeoff, as well all know by now, is towing; the Duramax in half-ton duty pulls a maximum 9,300 pounds in the Silverado. Rivals across town can do more, the Ford F-150 PowerStroke rated at 11,500, the Ram 1500 EcoDiesel game to pull 12,560. GM engineer John Barta told Muscle Cars & Trucks that more hauling chops could be on the way, explaining, "We’re actually looking at upgrading some of the materials around (the engine bay) to see if we can maybe raise our tow rating." Engine bay materials are at issue due to thermal complexities underhood. John Barta, GM's assistant chief engineer of diesel engine controls, said the Duramax's inline-six configuration allowed engineers to get emissions hardware like the combined selective catalytic reduction, diesel oxidation catalysts, and diesel particulate filter unit closer to the engine, where it heats up quicker, getting emissions down quicker. But that filter puts another heat source in those confines, enforcing a cap on the tow rating to keep the engine and other systems from overheating. "If you look under the hood," he said, "youÂ’ll see a significant amount of silver ‘moon tapeÂ’ around to make sure things arenÂ’t getting overheatedÂ… if we were to go up in higher towing, which we can, we start impacting the possibility of deteriorating some of the components.” There isn't much space for more grille, so swapping for a better grade of "moon tape" or a different kind of material could reduce engine bay heat, extracting a higher tow rating in the process.  It's important to note a point Barta's been making for months about the Duramax figures, though. "Even though itÂ’s nice to brag about big numbers, in reality, light duty customers are not towing that large with their trucks," and, "We do know that (95 percent) of our light duty customers donÂ’t tow over 9,000 pounds." On our First Drive of the 2020 Silverado diesel we called out the tow rating, but emphasized that the Chevy and GMC have more important challenges to overcome.